Various types of low-density materials have been employed in connection with structural materials, usually structural materials of a hollow type which may be partially or fully filled with such a low-density filler material for the purpose of reducing the overall weight of the combination and also for enhancing the thermal-insulating and/or acoustical insulating characteristics thereof. However, the use of laminated, low-density high-specific volume filler material in joined relationship to one or more convoluted weight-reducing, strength-increasing stiffening layers of structural formed material whereby to provide an effectively unitary high strength-to-weight ratio, structural panelling material has not been carried to its ultimate optimum in the past and certainly has not been provided with effectively built-in fire extinguishing means capable of preventing self-sustained or self-supporting combustion and of either preventing or greatly inhibiting combustion of such structural panelling material from combustion initiated, supported, and/or maintained by substantially more combustible adjacent materials or sources.
Thus, it is clear that the provision of such an effectively unitary high strength-to-weight ratio structural panelling material, including high strength corrugated stiffening portions and lower strength extremely low-density, high-specific volume filler material intimately fastened together in an area-coextensive manner and provided with built-in fire extinguishing means would be extremely desirable and it is precisely such a highly-desirable and advantageous type of structural panelling material which is provided by and in the present invention and which has major advantages completely overcoming prior art disadvantages and limitations (such as ready combustibility, the extremely exothermic nature of such combustion when started, and the production of extremely toxic gasses from such combustion of prior art filler foam plastic materials), and all of which advantages flow from and occur by reason of the specific features of the invention hereinafter.